The present invention relates to optically clear, cross-linked silicone polymers, to fast curing precursor compositions useful for producing such polymers, to intraocular lenses (IOLs), for example, injectable IOLs, and to methods of forming such IOLs. More particularly, the invention relates to such silicone polymers, fast curing precursor compositions, injectable IOLs and methods which provide substantial benefits, for example, silicone polymers and injectable IOLs which have reduced discoloration susceptibility.
Silicone polymers are known materials and many are known to be produced using platinum group metal-containing catalysts, which catalysts become an integral part of the final product. For example, certain silicone polymers are known to be useful in the production of IOLs. Also, certain curable liquid compositions comprising monomers which can be cured in the presence of platinum group metal-containing catalysts to form silicone polymers have been suggested for use in forming a solid, transparent synthetic lens upon being injected into the lens capsule of an eye from which the natural lens has been removed. Such solid, transparent synthetic lenses formed in the eye may be considered or termed "injectable IOLs". See, for example, Wright et al U.S. Pat. No. 4,608,050, which is incorporated in its entirety herein by reference.
Injectable IOLs which comprise cross-linked silicone polymers are cured or cross-linked in the eye, at physiological temperature, for example, about 35.degree.-37.degree. C. In order to obtain a desirably fast cure rate, relatively high levels of catalyst, in particular platinum group metal-containing catalyst, are used.
One problem that presents itself in the use of such fast curing liquid precursor compositions is that over time the resulting polymer tends to discolor. Such discoloration, which is believed to be associated with the relatively high platinum group metal-containing catalyst levels in the precursor compositions, is disadvantageous. Therefore, it would be advantageous to provide fast curing precursor compositions which yield polymers having a reduced susceptibility to discoloration.
Sierawski U.S. Pat. No. 4,122,246 discloses a silicone gel which discolors less on aging than other platinum catalyzed silicone gels. The disclosed silicone gel is prepared by mixing vinyl-containing polyorganosiloxane, a silicon-bonded hydrogen containing organosiloxane compound, a platinum catalyst, a polysiloxane having at least two vinyl radicals and at least one silicon-bonded hydroxyl radical, and an epoxy-containing alkoxy silane. The mol ratio of silicon-bonded vinyl groups to silicon-bonded hydrogen atoms in the vinyl-containing polyorganosiloxane plus silicon-bonded hydrogen containing organosiloxane compound is greater than 1, preferably greater than 1.1, while the mol ratio of silicon-bonded vinyl radicals to silicon-bonded hydrogen atoms in the entire mixture is preferably from 1.2 to 3.3. The presence of epoxy silanes in the polymerization mixture can result in quality control problems. For example, the epoxy silanes can provide large numbers of crosslinks which can result in products not having the desired characteristics. Also, injecting a mixture containing such epoxy silanes into the eye may have detrimental effects on the eye. Therefore, it would be advantageous to provide fast curing precursor compositions, e.g., useful for injection into the eye, yielding silicone polymers which have reduced susceptibility to discoloration without the need to include epoxy silanes.